Liquid crystalline polyesters have excellent heat resistance, excellent flowability and excellent dimensional stability because of their liquid crystalline structure. The demand for liquid crystalline polyester has accordingly been expanded especially in the application of small-size electric and electronic components that require such properties. Polyphenylene sulfide (hereinafter may be abbreviated as PPS), on the other hand, has excellent heat resistance, excellent chemical resistance and excellent electric insulation and is used for various electric and electronic components, machine components and automobile components.
Printing characters, symbols, patterns and a barcode on the surface of a molded product made of a resin composition is widely performed for the purpose of identification of the molded product in, for example, the production process or for the purpose of decoration of the surface of a product. Ink marking, however, has problems such as insufficient adhesion of a coating material and the complicated treatment process. Recently, simple and efficient marking method using laser beam radiation (laser marking) has accordingly received attention. The laser marking technique is a marking method by foaming or carbonizing the resin with laser radiation. This technique eliminates the problems of ink marking regarding, for example, adhesion of a coating material and a complicated treatment process.
The following techniques have been proposed to improve the laser marking property. For example, known techniques include a method of adding a copper salt absorbing laser beam such as copper phosphate or copper sulfate (see, for example, U.S. Pat. No. 5,489,639), a method of adding an alumina hydrate (see, for example, JP 2005-162913A), a method of adding mica and a metal sulfide (see, for example, WO 2005/26247A) and a method of adding a phthalocyanine-based colored colorant (see, for example, JP 2005-199626A). These additions have improved the laser marking property to some extent.
Applying the above techniques to a resin composition including a liquid crystalline polyester and/or a polyphenylene sulfide having high heat resistance, however, causes the following problems. Specifically, the additives added for the purpose of improvement of the laser marking property are degraded, for example, during the molding process under high temperature condition. This accordingly causes the problem that the molded product does not sufficiently absorb laser beam radiation and does not achieve clear marking. Degradation of the additives also causes the problem of a decrease in heat resistance, for example, reduction in viscosity in the high-temperature retention state, blister in the reflow process and an increase in warpage.
It could therefore be helpful to provide a thermoplastic resin composition having high heat resistance and high laser marking property and its molded product by using a liquid crystalline polyester and/or a polyphenylene sulfide having excellent heat resistance.